This invention relates to wheel and bearing assemblies for conveyors and other applications and, more particularly, to wheel and bearing assemblies including wheels or bearing members formed from thermoplastic material and including bearing seals formed from thermoplastic material fused to the plastic wheel or bearing member.
Sealed wheel and bearing assemblies for conveyor and other applications utilizing various types of bearing seals are well known. A common use for many sealed wheel structures is in conveyor applications such as in trolley conveyors for the food handling industry. Such conveyor wheels are subjected to many different environmental conditions such as water sprays for cleaning, extremes of temperature in various food processing operations, and the like. Many prior known sealed wheel structures have been unable to provide complete and effective protection for the internal bearing areas in such environmental conditions. For instance, prior sealed wheels would often admit water therewithin under high pressure water spray conditions which would dilute the bearing lubrication causing wear and corrosion of the bearing surfaces and generally shorten the useful life of the structure.
Another common problem with prior known sealed wheel structures is that of separation of the seals from the wheel during operation. In those wheel structures where the seal attachment was relatively insecure, use of the structures in high speed operation would often cause the seals to loosen or completely separate from the wheels.
Further, many of the prior known sealed wheel and bearing structures utilizing either metal or plastic wheels and metal and/or plastic seals were difficult to manufacture. Typically, prior known seals were held on wheel or bearing structures in reverse taper, inwardly diverging grooves which required the seals fitted therein to have either precise tolerance dimensions or spring-like resiliency for flexing and insertion in the grooves.
Certain attempts were made at using plastic seals held in such grooves. However, because plastic is extremely difficult to hold to precise tolerance dimensions during molding or other forming operations, such seals were not highly effective. Spring-like seals tended to place additional drag on the opposing surface being sealingly engaged. This caused greater wear and a shorter life for the structure. In the case of manufacturing reverse taper grooves in metal wheels or bearings, such seal holding grooves were difficult, time consuming and expensive to machine. In plastic wheels, such reverse tapered, seal holding grooves were difficult to mold.
It was also detrimental to weld metal seals in place because welding heated the races of the metal wheels or bearing causing annealing and softening which decreased the useful life of the structure.
A need arose, therefore, for sealed wheel or bearing structures which could completely and effectively seal out moisture, dirt and other foreign particles or contaminants in various environmental conditions and yet would be wear resistant, have a long life, would hold together and not separate even under high-speed operational conditions, and would be simple and inexpensive to manufacture. The present invention was designed to overcome the above problems and to fill the indicated need.